How to take the Cage Swing to the Games

I have been working with a hitter for awhile now, in the cage his swing is really nice, power extension and even releases his top hand 100% of the time. I went and watched him play and 100% of the time he does "not" release his top hand in games or scrimmages? How can you get a player to take what he does in the cage and apply it in games. I have had him hit off a machine, thrown from as far back as 50 feet, even wore a full uniform once, but again we were in the cage. I even see him taking warmup cuts on deck releasing the top hand.

My next step is to go out to a field and throw from 60 feet and see if that will get him to take the cage swing to the field. Only other thing I can think of is get a friend to throw live BP off the mound.

Any suggestions? Other than putting vaseline on his top hand, don't think I haven't thought about that.